Optical surgical probes deliver light to a surgical field for a variety of applications. In some applications, it may be useful to deliver light to multiple spots in the surgical field. For example, in pan-retinal photocoagulation of retinal tissue, it may be desirable to deliver laser light to multiple spots so as to reduce the time of the pan-retinal photocoagulation procedure. Various techniques have been employed to produce multiple beams for a multi-spot pattern. For example, one approach uses a diffractive beam splitter element to divide an incoming beam into multiple spots that are coupled into multiple optical fibers that deliver the multiple spots to the retina. But it is also desirable to have a multi-spot generator that can be placed at a distal end of the optical surgical probe to more easily produce multiple spots from a single input beam, so that the multi-spot generator can more easily be used with existing laser sources without the need for additional components to align the laser surgical probe with the sources.
Difficulties can arise in the use of a diffractive beam splitter element at a distal end of the optical surgical probe. As one example, a diffractive beam splitter element produces a multitude of higher diffraction orders, and while these orders are relatively lower in light intensity as compared to the primary spot pattern, they may not always be negligible in terms of their effects. As another example, a diffractive element may not perform identically in different refractive media. For example, if the diffractive beam splitter element is placed into a medium other than air, such as saline solution or oil, the recessed portions of the microscopic surface relief structure of the diffractive beam splitter element can be filled with material having a different refractive index than air, which can ruin the spot pattern. As yet another example, the spacing between the spots can vary for different wavelengths, which can be problematic when an aiming beam is of a certain color while a treatment beam is of a different color. Lastly, diffractive elements are frequently expensive and difficult to produce, and this is particularly the case when the diffractive element must be constructed to fit into a small area, such as a distal tip of a surgical probe for surgical instruments that are 23-gauge or smaller. Thus, there remains a need for an optical surgical probe that can produce multiple spots at a target area using optical elements at a distal end of the surgical probe.